This invention relates to a method for manufacturing microwave circuit devices, and to a microwave electric filter manufactured in accordance with that method.
Microwave devices have typically been fabricated by manufacturing individual parts and assembling those parts. This is usually a costly operation, and products produced thereby are often rather bulky in size. Some examples in the interdigital, or comb-line, filter art are included in the following three patents. An R. E. Fisher U.S. Pat. No. 3,818,389 shows an interdigital filter arrangement for a microwave mixer in which two filter portions share a common output coupling element. Fine-tuning is accomplished by tuning screws extending through cavity walls toward interdigital, hollow, conductive resonator rods, or strip-line conductors. Conductive wall members are assembled to form a microwave cavity enclosing the resonator rods. A G. L. Burnett et al. U.S. Pat. No. 4,037,182 shows a microwave tuning device in which a tuning screw is inserted through an insulator ring in a cavity wall and into a recess in the end of a resonator rod. The ring physically stabilizes the end of the rod to eliminate a tuning fork effect. The rod recess increases the tuning range of the filter. This type of device is employed in a single comb-line filter in which the cavity walls which are parallel to the rods are spaced closely enough to suppress propagation modes higher than that employed for the filter. The rods are somewhat less than one-eighth of a wavelength in length. Rod diameter is determined by the requisite susceptance. Coaxial conductors are attached perpendicularly to end rods of a comb-line and provide input/output functions. Another G. L. Burnett et al. Pat. No. 4,112,398 provides a lightweight microwave filter of the interdigital, or comb-line, type in which a lightweight, temperature-sensitive, metal cavity encloses resonator rods. Each rod is formed of two segments: a high-temperature-sensitivity segment and a low-temperature-sensitivity segment. The segments are proportioned so that thermal dimensional effects compensate, i.e., capacitance changes between rods and the cavity wall offset resonant frequency changes of the rods in response to temperature changes.
Dielectric materials are sometimes employed in microwave filters for various functions. For example, data sheets for the Panasonic Industrial Company microwave dielectric duplexer EYU D835C8801 and microwave bandpass filters EYU FOR835401 and EYU FOR880601, each includes a general statement that a dielectric coaxial resonator is employed. Also, an A. Kivi et al. U.S. Pat. No. 4,053,855 shows the employment of a dielectric material to fill the spaces among resonators in a resonant cavity filter for reducing the likelihood of multipacting in the filter.